Source: cirosantilli/liquid-helium

= Liquid helium
{title2=4.2 K}
{wiki}

= Helium I
{synonym}
{title2}

4 K. Enough for to make "low temperature <superconductors>" like regular metals superconducting, e.g. the <superconducting temperature of aluminum> if 1.2 K.

Contrast with <liquid nitrogen>, which is much cheaper but only goes to 77K.